Police have opened an investigation after a letter containing a suspicious-looking white powder arrived at Holyroodhouse in Edinburgh, the Queen’s official residence in Scotland.

A preliminary look at the letter confirmed that it poses no threat to the general public and citizens of Edinburgh.

“We can confirm that the suspicious letter that was delivered to the Palace of Holyroodhouse on Wednesday, June 7 has been analyzed and found not to pose any risk to the public,” a Police Scotland spokesperson said Wednesday, according to the BBC. “An investigation is now underway to identify the sender and establish the full circumstances surrounding this incident.”

As the letter was being received, tourists and guests were still visiting Holyroodhouse. Roads around Holyroodhouse were closed off this morning, with ambulances and fire trucks sitting outside.

This is the second instance of such a letter being sent to a notable location in Edinburgh. Last month, another letter with similar white powder was sent to Scottish National Party headquarters (the party of Scotland’s First Minister Nicole Sturgeon), a close neighbor of Holyroodhouse.

A royal spokesperson confirmed the monarch was not at Holyroodhouse when the letter was received. She is at her London home, Buckingham Palace.